Hello everyone, my name is Diego Rodriguez. I am a research specialist under the
supervision of Dr. Hans Stein, and today I will talk about research that I conducted in my
master program at the University. So the study we conducted was about the effect of
extrusion on nutrient and energy digestibility in cereal grains fed to growing pigs. 

This is the outline of this presentation. First, I will talk briefly about the extrusion
process and the effect that may have on feed ingredients where they are extruded. Then I
will move on to the materials of method of this study that we conducted, showing some
results, and by the end, some conclusions. 

Extrusion is a feed technology that is commonly used in the pet food industry or aqua
feed. It is known that about 95% of pet food is extruded. However, this technology is not
extensively used in the swine industry because of the high cost of this process. The
purpose of extrusion is mainly cooking followed by an expansion of the raw material, and
therefore this process may facilitate enzymatic activity in the digestive tract. This
process combines the use of moisture and heat during the conditioning step of the raw
material. And after that, by combining mechanical forces such as pressure and friction,
the raw material will be extruded. After this process after the material was extruded,
there is the last step, which is the drying and cooling of the material. And this process
may have done in the right temperature and time to avoid retrogradation of the starch,
meaning that we are forming resistant starch, which is going to be difficult to absorb in
the small intestine, and therefore it will be fermented in the hindgut. 

The effect of the extrusion process in feed ingredients in terms of handling properties
are that the bulk density may be reduced, which is not desired because of the storage
efficiency. That means that we will store less feed in the same volume. Also, due to the
high temperatures that is used during the extrusion, there is a reduction of
microorganisms that could be present in the feed ingredients. In term of digestibility of
nutrients, there has been reported an increase in starch gelatinization after the
extrusion process. 

To understand a little bit better what is starch gelatinization, first, starch is a
polysaccharide, which is the main energy reserve in plants, and it is usually present in
high content in cereal grains. It is composed of a polymer of glucose that can form linear
chains of glucose to form amylose, or a branched chain to form amylopectin. Usually,
cereal grains are composed for about 25–30% of amylose and 70–75% of amylopectin. The
first physical change in the starch granules, when it is exposed to heat and moisture, is
that the amylose crystallinity starts to break up and the granule starts swelling until it
reaches a point when the amylose starts diffusing out of the granule, forming a gel around
the particle and leaving most of the amylopectin inside of the starch granule. So this
process may increase the viscosity of the ingredient and make the starch most digestible,
and that is because amylose is out of the particle and it gets more easier and more
accessible to the digestive enzymes. 

By having an increase in starch gelatinization, starch digestibility will be increased as
well. Also, it's been reported that by extrusion process, energy digestibility will be
increased. On the other hand, the effect of extrusion in amino acid digestibility is not
constant because of the variability in the temperatures and time that is used during the
extrusion process. And that is because high temperatures may increase denaturation of
protein, especially the amino acid lysine, due to the Maillard reaction. 

Therefore, the objectives of this study were to test the hypothesis that extrusion of
cereal grains may increase ileal digestibility of amino acid and starch as well as an
increase the apparent total tract digestibility of fiber and gross energy. And also, an
increase in the concentration of digestible and metabolizable energy. 

Now let's move on into the materials and methods of this study. 

For this study, we utilized three different cereal grains—corn, wheat, and sorghum—that
were ground to have a particle size of around 500 microns. And each grain was divided into
two batches. So, the first batch was used without any further process, whereas the second
batch was extruded. Therefore, we had six different treatments for this study. 

To test our hypothesis, we conducted two different experiments. The first experiment was
to determine the effect of extrusion in amino acid digestibility, and the second
experiment was to determine the effect of extrusion in nutrient digestibility. For the
first experiment, we utilized seven cannulated barrows with initial body weight of 14 kg.
And for this experiment, we formulated six different diets containing around 93% of
inclusion of one of the each cereal grains as the only source of amino acid. Also for this
experiment, we formulated a nitrogen-free diet to determine the basal endogenous losses of
amino acid from the pig. For the second experiment, we utilized 48 growing barrows with
initial body weight of around 15 kg. And for this experiment, we formulated six diets
containing around 97% of inclusion of one of the each cereal grains as the only source of
energy

Now let's move on into the results for this study. 

Before I continue with this presentation, I will set up the slides that I'm going to use
for the most part of this presentation. In blue colors, corn will be represented, wheat
will be represented in orange colors and sorghum will be represented in green colors,
where the dark colors will be the cereal grains that were used with no extrusion and the
light color will be the cereal grains that were extruded. Cereal grains that were not
extruded had a moisture content of around 12% but, after extrusion, there was a reduction
of moisture content in all cereal grains. This effect was expected due to the drying
process that is done during the last part of extrusion. For this reason, I will present
the data based on 88% of dry matter so we can observe more accurately the difference
between the cereal grains that were extruded or not extruded. 

Now we are looking at the effect of extrusion in fiber. Neutral detergent fiber in corn,
wheat and sorghum were about 8–12%, whereas less NDF was analyzed in the extruded cereal
grains. A similar trend was observed for the acid detergent fiber; non-extruded cereal
grains had greater ADF concentration compared with extruded cereal grains. This means that
the most fermentable part of the fiber in the three cereal grains were solubilized, and
therefore the less fermentable part of the fiber was left in the cereal grains after the
extrusion. 

In terms of protein quality, we analyzed crude protein, and it was observed that there was
not a reduction of crude protein after the extrusion process. However, because of the heat
treatment during extrusion, we wanted to see if there was a damage in amino acids. So we
calculated the lysine to crude protein ratio to observe if there was any damage of lysine
due to the Maillard reaction, and it was observed that the lysine to crude protein ratio
did not change after the extrusion process. That means that the extrusion in this case was
performed in a good quality. 

Of course, we have to look the gelatinization of the starch because the main purpose of
extrusion is the starch gelatinization. We observe that the total starch in the three
cereal grains was about 60%, which was expected based on the literature. And among the
total starch for each cereal grain, we observed that less than 10% of that starch was
gelatinized before the extrusion process. 

However, with similar concentration of starch, the extruded cereal grain had more
gelatinized starch. And we observed that the total starch that was gelatinized was more
than 90% of the total starch. 

Now, we are looking at the gross energy in cereal grains and we observed that there was an
increase in gross energy in all three cereal grains. That may be because after the
extrusion process, the primary structure of the particles was changed due to the expansion
of the material and therefore more gross energy was analyzed. 

Let's move on into the digestibility part. Before that, let me also set up the slides. So
from now to the end of this presentation, non-extruded cereal grains will be represented
in blue bars and extruded cereal grains will be represented in orange bars. The apparent
ileal digestibility of starch, we observed that there was no interaction between extrusion
and the cereal grains. However, the AID of starch in non-extruded cereal grains was about
90% and by extruding, the AID of starch increased almost up to 99%. And this may be
explained because of the increase in starch gelatinization of the cereal grain. 

There was an interaction for the standardized ileal digestibility of crude protein between
cereal grains and extrusion process, and we observed that the corn that was extruded has
greater SID of crude protein compared with the non-extruded corn. However, this effect was
not observed for wheat and sorghum.

We also wanted to see the effect of the individual amino acids. And we observed that for
digestibility of lysine, there was no interaction between cereal grains and extrusion
process. However, after extrusion, there was an increase in SID of lysine in all three
cereal grains compared with non-extruded cereal grains. And for this case, we expected a
reduction of lysine due to the Maillard reaction and the high temperature that is usually
used during the extrusion process. However, in this case there was not any damage of
lysine after the extrusion process. In terms of digestibility of methionine, we have said
that there was an interaction between cereal grain and extrusion. And it was observed that
extruded corn had greater methionine digestibility compared with non-extruded corn, but
there was not any difference after the extrusion for wheat and sorghum. 

The same trend was observed for threonine and tryptophan digestibility. And we observed
that there was an interaction between cereal grain and extrusion process. And it was
observed that there was an increase in digestibility of these two amino acids for extruded
corn compared with non-extruded corn. However, there were not any difference for wheat and
sorghum after the extrusion process. 

Now we are looking at the apparent total tract digestibility of gross energy. And we
observed that there was an interaction between extrusion and cereal grain. And it was
observed that after the extrusion process, there was no difference for the extruded wheat
or non-extruded wheat. However, there was an increase in apparent total tract
digestibility of gross energy after the extrusion process in corn and sorghum. 

There was an interaction between cereal grains and extrusion that digestible energy was
increased by the extrusion, but the degree of increment was less in wheat compared with
sorghum or corn. And the same was observed for metabolizable energy, that the effect of
extrusion was greater in corn and sorghum compared with wheat. So from this data, more of
the effect that was present was found in corn and sorghum in term of digestibility of
amino acid and energy and the concentration of digestible and metabolizable energy
compared with the effect of extrusion in wheat. Based on the literature, the structure of
wheat in term of starch and fiber is more complex compared with the structure in corn and
sorghum, and that means that during the extrusion process and the process of expansion of
the raw material, it is more difficult to have an effect on starch due to the organization
of the starch inside of the kernel of the wheat. 

Now we are looking in terms of digestibility of fiber. And we observed that there was no
interaction between cereal grain and extrusion. However, by extrusion of cereal grains,
the apparent total tract digestibility of ADF decreased in all three cereal grains. In
terms of digestibility of NDF, we observed that there was an interaction between cereal
grain and extrusion. And we observed that the digestibility of NDF in wheat decreased
after the extrusion process compared with the non-extruded wheat. And this reduction in
digestibility of fiber may be because after extrusion process, the most fermentable part
of the fiber was solubilized and therefore the less fermentable was remain in the cereal
grains, and therefore there is a reduction of fiber digestibility. 

So now let's move on into the conclusion for this study. 

After this study, we can conclude that concentration of fiber may be reduced after the
extrusion process. However, concentration of gross energy may be increased after the
extrusion process. And in this particular experiment, we can conclude that the extrusion
process did not change the concentration of amino acid in cereal grains. In terms of
digestibility, we can conclude that apparent ileal digestibility of starch, standardized
ileal digestibility of amino acid, apparent total tract digestibility of energy, and
concentration of digestible and metabolizable energy was increased after the extrusion
process. However, this increase depends of the type of the cereal grains, and also it
depends of the composition of starch and fiber in cereal grains. 

Thank you so much for listening to this presentation, and if you would like to know more
about our work in our lab, you can visit our website. Thank you.